In mineral and oil exploration, borehole logging is used to determine the subsurface content of rocks and mineral deposits.
Nuclear logging tools provide valuable data to the oil industry and have been used in oil well logging for more than 30 years. Data on the porosity and density of rock formations, which is used to help detect the presence of geological reservoirs and their contents (e.g. oil, gas or water), form one of the log suites used in oil well logging.
The existing digital pulse processing techniques employed in borehole logging rely on linear filtering methodologies. However, with increasing count rate, the high-pass filters required to shorten pulse length and increase throughput also degrade signal-to-noise ratio (SNR), and ultimately, energy resolution. This limits the count rate that can be employed, the strength of the source, the proximity of the source and detector, or combinations of these parameters. In bore-hole logging applications, for example, overall measurement time is very important. The information lost due to the discarding of pile-up events extends the collection time required to obtain sufficient accuracy in the estimation of elemental concentration and ultimately places an upper limit on the speed at which a well can be logged. U.S. Pat. No. 4,883,956, for example, assesses the benefits of a new radiation detection crystal, cerium-doped gadolinium orthosilicate (GSO). The decay time of GSO detectors results in less pile-up for any particular count-rate, or accommodates a higher count-rate for a particular acceptable pile-up.